Photoelectric effect

The emission of electrons from a material after it absorbs electromagnetic radiation. In the external photoelectric effect, electrons escape the material’s surface when the radiation’s frequency is high enough.

Photon: A quantum of electromagnetic radiation that carries energy and momentum. Einstein explained the effect by treating light as discrete energy-carrying quanta.
Heinrich Hertz: German physicist who demonstrated the production and detection of electromagnetic waves in the 1880s. His spark-gap experiments revealed that ultraviolet light could affect electrical discharge.
Photocell: A device that converts incident light into an electrical signal or change in electrical behavior. Photocells use photoemission or related light-induced effects to detect illumination.
Compton scattering: The scattering of a photon by a charged particle, with a change in photon wavelength. It also demonstrates photon momentum, but the photon is scattered rather than absorbed to eject an electron.
Work function: The minimum energy needed to remove an electron from a material’s surface. It sets the minimum photon energy required for electron emission.
Philipp Lenard: German physicist who studied electrons emitted from metals under ultraviolet illumination. His measurements established key features that classical wave theory could not explain.
Photomultiplier tube: A vacuum tube that amplifies weak light signals through photoemission and electron multiplication. Its photocathode releases electrons that are multiplied into a measurable current.
Photoconductivity: An increase in a material’s electrical conductivity caused by absorbed light. Light changes conductivity here without necessarily ejecting electrons from the material.
Threshold frequency: The lowest radiation frequency that can produce a specified physical response in a material. Below this frequency, individual photons cannot overcome the material’s work function.
Albert Einstein: Theoretical physicist who introduced the light-quantum explanation of the photoelectric effect in 1905. He explained the frequency threshold and electron energies using quantized light.

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